Micromechanical devices generally include miniature devices manufactured upon a substrate with moving parts. One example of such a device is the digital micromirror device, or DMD, manufactured by Texas Instruments of Dallas, Tex. Other examples include microaccelerometers, micromotors and gears. Some of these structures include a support member from which another component of the micromachine is suspended, such as a hinge or beam.
The repeated movements of the suspended components require a hinge or beam that is elastic yet robust. The flexibility is required so as to allow the suspended component to move. If the hinge or beam is not robust, it could become permanently twisted in the direction of movement, or be deformed plastically so as to change its dimensions.
Various theories have been proposed to explain this behavior, including microslip of dislocations, heavier oxidation at grain boundaries on one side compared to the other, or even the development of surface films.
The use of alloys of aluminum with nitrogen and other elements to form mixtures of ordered compounds has been proposed. For an example of these types of compounds, reference is made to commonly assigned patent application Ser. No. 5,552,924, entitled "Micromechanical Device Having an Improved Beam." The goal in these types of processes was to develop some type of intermetallic with more slip resistance than face-centered cubic (FCC) crystalline structures. Nitrided aluminum and non-aluminum alloys can also be used to form a metal film from which an elastic member is formed, either as polycrystalline film or amorphous film. An example of these types of compounds is disclosed in the cross-referenced commonly assigned patent application Ser. No. 08/706,374, entitled "Improved Elastic Member for Micromechanical Device." The teachings of both of these patent applications is incorporated herein by reference.
It has been observed using some well known deposition systems that films prepared to function as hinges or beams typically show varying degrees of stress relaxation when strained to 1%. The stress relaxation can be viewed as creep and is a function of the structure and possibly the density of amorphous films. Material with low or no stress relaxation is considered best. Although the recrystallization temperature of these amorphous films increases with nitrogen content, the stress relaxation is not a simple function of nitrogen. Intentionally nitrided films, i.e. whereby nitrogen is added in the sputter gas, has lower stress relaxation when nitrogen gas is increased to 10%, but increased stress relaxation when the nitrogen percentage is increased to 20%.
It is desired to further improve the stress relaxation of TiAl.sub.3 amorphous films.